Fig. 3
Experimental apparatus for mode excitation and characterization. a Experimental apparatus for excitation and characterization of angular momentum fiber modes. b Near field image of the fiber under test with a pure |J| = 5, ↑↓ mode excited. c Two independent time of flight measurements showing selective excitation of SOI pairs |J| = 5, ↑↑ and |J| = 5, ↑↓, and d time of flight measurement of |J| = 5, ↑↓ on log scale, showing 20 dB+ suppression of the SOI pair. e Measurement of the far field of the |J| = 5, ↑↓ mode from (d) after splitting in polarization and propagating through an axicon, which converts angles to position. Two different ring sizes, corresponding to different free space OAM states, are observed as expected. f Reciprocal setup for transmission matrix measurement
